1. Field of the Invention
This invention relates generally to the manufacture of textile articles, such as carpet and synthetic turf products. More specifically, the invention relates to an oven used to cure adhesives to the back of textile articles.
2. Related Art
It is well known to prepare textile articles having a pile surface, such the tufted side of a carpet and synthetic turf, by binding natural or synthetic fibers to a primary backing material by the means of a thermosetting adhesive. Secondary, tertiary and further backing materials may also be utilized and may be similarly bound to prior backing materials, to the fibers, or to both by means of a thermosetting adhesive. To bind the backing material to fibers, to other layers of backing material, or to both, the back surface of article is coated with a layer of thermosetting adhesive. The thermosetting adhesive is then heated to a sufficiently high temperature so that it achieves a liquid or plastic state and penetrates the interstices of the fibers, the respective layer(s) of backing material, or both. An effective method for heating the thermosetting adhesive is to pass the textile article, coated with the thermosetting adhesive, through an oven. However, the thermoplastic fibers and backing materials have softening temperatures in the same general range as the temperatures required to heat the thermosetting adhesives. Typically, the softening point of thermosetting adhesives used to anneal fibers to the primary backing is between approximately 180° F. and 250° F. The softening point of thermoplastic fibers used for artificial turfs is typically less than 176° F. (80° C.). For example, Thiolon™ polyethylene fiber, a preferred fiber used in artificial turfs, softens at temperatures greater than 150° F. (65.5° C.) and fiber shrinkage is 1.2% at 158° F. (70° C.). Thus, the manufacturer recommends that that coatings be applied at the lowest possible temperature and Thiolon™ fibers not be exposed to temperatures in excess of 194° F. (90° C.).
Tunnel ovens, such as those described in U.S. Pat. Nos. 6,944,968, 6,121,166 6,180,166, 5,045,375, and 4,390,585, are particularly suitable for bonding a thermosetting adhesive to a textile article, and such ovens are commercially available from various manufacturers such as Schott & Meissner, FECO and Glenro. Transport assemblies for transporting articles through a tunnel oven are well known in the art and commercially available, preferably having continuous loop flexible chain linkage means for rotational movement of parallel, laterally extending rollers, such as a conveyor assembly. The transport assemblies also include well known devices to support and secure the textile. The support means preferably comprise stenter or tenter frames, such as those described in U.S. Pat. No. 4,788,756, or other similar support means movably connected to the transport assembly.
Multi-pass tunnel ovens that have transport and support assemblies and allow an article to pass through the oven more than once, in a loop fashion, are also well known in the art and are commercially available. Such multiple-pass tunnel ovens permit extended heating times without requiring longer oven housings. Due to the benefits of a relatively shorter length and an extended heating time, a multi-pass tunnel oven having upper and lower transport means and support means disposed to permit an article to pass through the oven twice in a loop fashion, is preferable over other oven configurations.
Various means may be used to provide heat in such ovens, including microwave energy, radiant heat (as described in U.S. Pat. No. 3,150,024), convection heat (as described in U.S. Pat. No. 4,604,491), hot air impingement, heated platens (as described in U.S. Pat. No. 4,174,991), ultrasound energy (as described in U.S. Pat. No. 6,720,058), and heated drums or rollers (as described in U.S. Pat. App. Pub. 2006/001389 and U.S. Pat. Nos. 4,652,322, 3,673,034 and 2,891,279). Heat may be generated by gas burner, steam, hot water, electrical heating elements, infrared heat lamps, ultrasound generators, microwave generators, infrared radiation generators or various other heat generating means that will be apparent to those possessing ordinary skill in the art. Air impingement tunnel ovens that are heated by gas burners are particularly suitable for purposes of the present invention.
It is often desirable to use combinations of fibers and thermosetting adhesives, where the temperature necessary to effect a sufficiently liquid or plastic state of the thermosetting adhesive is higher than the temperature at which the fibers will burn, soften, shrink or otherwise be damaged. It is particularly common in the manufacture of artificial turf for fibers to shrink or curl, resulting in a product that is lower in quality and may be less functional, less aesthetic, or both. Furthermore, to compensate for anticipated shrinkage, fibers that are longer than the desired post-heated length must be used in the pre-heated article, thereby increasing the cost and the weight of the product.
To minimize the effects of heating the fibers, prior art ovens and heating systems have employed split heat zones within the oven. In certain heating systems, the article passes sequentially through one or more heated zones and then sequentially passes through one or more separate cooled zones. However, such systems do not permit simultaneous heating of the thermosetting adhesive on the back surface with the cooling of heat-sensitive fibers on the pile surface and subsequent cooling is not generally effective to prevent or reverse the shrinkage, curling and other undesired effects on the fibers that occur in the heated zones.
Some prior art split zone ovens allow for separate heating of a top zone and a bottom zone within the oven, such as in the CTS/Gyson True Zone oven, so that the thermosetting adhesive covered back surface of the textile article may be heated to a higher temperature than the more temperature sensitive pile surface of the article. However, prior art ovens merely recirculate the air in both of the respective zones so there is no active cooling with a positive pressure differential from the cooler zone to the hotter zone nor are there exhaust ports for directly venting the cooling air without recirculation. In yet another form of a prior art split zone oven, the article passes through the oven with only the back surface exposed directly to the heat source, such as with a single air impingement oven. In such prior art split zone ovens, the heat from the higher temperature zone may leak or flow into the less heated or unheated zone at various locations along the transport frame, thereby raising the localized temperature of the pile surface at these locations and causing shrinkage and warping of the fibers.
Physical barriers have been developed in an attempt to substantially separate the heated and lesser heated or unheated zones, and to deter hot air leakage or flow into areas in which the tufted surface passes. Current barriers include metal plates or heat-resistance cloths that run the length of the oven in the same plane as the transport assembly, and are positioned between the oven walls and the support or transport system. However, physical barriers alone do not sufficiently prevent hot air from leaking into less heated or unheated zones, and this leakage can damage the pile side of the textile, particularly along the edges as well as other localized heating regions that may also damage the pile surface. Additionally, heat-resistant cloths may become worn and develop tears further diminishing the barrier function. Thus, known means to separate heated from less heated or unheated zones within ovens are not completely effective in maintaining the tufted surface at a sufficiently low temperature and eliminating shrinkage, curling, and other undesired effects on heat-sensitive fibers.
To date, there is no known oven that permits active cooling of the pile surface of a textile article while simultaneously heating the thermosetting adhesive covered back surface of such article. Without the present invention, current ovens can shrink polyethylene fibers by approximately ¼″ for a pile that is about 2¼″, resulting in more than 5% shrinkage. Thus, there is a need for an oven that has the capability to heat the thermosetting adhesive to a sufficiently high temperature so that the adhesive softens or melts and flows into the interstices of the fibers, layer(s) of backing material, or both, while simultaneously protecting the pile surface of the textile article so as to reduce or eliminate warping, shrinkage and any other undesired alteration of the fibers.